1. Field of the Invention
The present disclosure relates to a liquid crystal display device, and particularly, to a gamma voltage generating circuit capable of increasing a gamma point without an addition buffer and without increasing a chip size, and a liquid crystal display (LCD) device including the same.
2. Background of the Invention
A flat panel display (FPD) is an essential display device for realizing a small, lightweight system such as portable computers, e.g., a notebook computer or a PDA, as well as a desktop computer, or a cellular phone terminal, to replace a conventional cathode ray tube (CRT) display device. Currently commercialized flat panel display devices include an LCD device, and a plasma display panel (PDP), an organic light emitting display device. Among them, LCDs have come to prominence as display devices used in mobile devices, monitors of computers, and HDTVs due to advantages thereof such as excellent visibility, ease in a reduction in thickness, low power consumption, and low heating.
A general display device includes a gate driver generating a gate driving voltage upon receiving a control signal from a timing controller, and sequentially supplying the generated gate driving voltage to gate lines to turn on thin film transistors (TFTs) connected to the gate lines, a data driver receiving a control signal and image data from the timing controller and applying a data voltage to the image data to a data line, and the timing controller controlling the gate driver and the data driver.
In particular, the data driver converts an input image data of a digital waveform into a data voltage of an analog waveform by using a predetermined gamma voltage. Here, the gamma voltage is an analog voltage corresponding to a gray level value of each image data, and a gamma voltage generating circuit generates a plurality of positive and negative gamma voltages respectively corresponding to gray level values and supplying the generated positive and negative gamma voltages to the data driver, and the data driver converts the image data into a data voltage by using a corresponding gamma voltage and outputs the converted data voltage.
FIG. 1 is a view schematically illustrating a gamma voltage generating circuit provided in a related art liquid crystal display (LCD) device.
Referring to FIG. 1, the related art gamma voltage generating circuit 40 includes a first resistor string 41 in which a plurality of first resistors R1 dividing two reference voltages Vref1 and Vref2 are connected in series, a decoder unit 45 selecting voltages divided by the first resistor string 41 by a selection signal SEL to generate a predetermined number of gamma reference voltages, a buffer unit 46 outputting the generated gamma reference voltages, and a second resistor string 47 in which a plurality of second resistors R2 dividing the gamma reference voltages to generate a plurality of gamma voltages GMA0 to GMA 255 are connected in series.
Since the gamma voltage generating circuit 40 having the foregoing structure may selectively generate the gamma reference voltages by using the divided voltages input to the decoder unit 45, the gamma voltages may be easily adjusted, compared with an existing scheme of using a variable resistor.
In the gamma voltage generating circuit 40, the output buffer unit 46 is provided to uniformly maintain a voltage level of a gamma reference voltage to generate a stable gamma curve with a minimized error. The output buffer unit 46 is connected to five gamma points P1 to P5 and outputs five gamma reference voltages to the second resistor string 47. Thus, the decoder unit 45 is formed as at least five decoders (not shown), and the buffer unit 46 needs to include five output buffers ob1 to ob5.
Thus, in a case in which a gamma reference voltage is intended to be added in order to minutely adjust a gamma curve, a separate gamma point should be defined and a buffer connected thereto should be added. This inevitably leads to an increase in component unit cost due to the increase in the number of buffers, and an increase in an IC size in which the gamma voltage generating circuit is integrated.